This invention relates to a photo-sensor array apparatus, and more particularly to a structure of arrangement of junction electrodes to be formed on a photo-semiconductor.
In recent years, various solid-state facsimile transmission devices incorporating a lens and an IC-based image sensor such as MOS or CCD in combination have been developed for practical applications with a view to improving the operational speed and reliability of the facsimile.
These devices are designed to operate on a common principle that the image of an original for transmission is focussed by a lens to form a reduced image on an image sensor. Consequently, the length of a light path is large and the size of the device is proportionately large, and the installation of the lens and the sensor requires high accuracy. The devices, thus, have disadvantages from the mechanical point of view. To be specific, as illustrated in FIG. 1, an original 2 for transmission is illuminated by a light source 1 such as a fluorescent lamp during main and sub-scannings and the beams of light reflected on the original are focussed by a lens 3 to form a reduced image on the image sensor surface of an IC sensor 4 and this reduced image is subjected to photoelectric conversion. When the size of the original 2 is about 220 mm and that of the sensor 20 mm, for example, the reduction ratio is 1/10. When the lens 3 in use has a focal length of 50 mm, the path of light from the original 2 to the IC sensor 4 measures about 600 mm in length. Thus, the device as a whole has a fairly large size. If, in the optical system just mentioned, the focal length is assumed to be 50 mm and the reduction ratio to be 1/10, then the depth of focus is small. This makes inevitable the provision of an adjusting mechanism which can aid in settling the IC sensor 4 in the device with high accuracy. It is further necessary to secure uniform distribution of light and uniform resolution on the entire surface of the original 2. Use of the lens 3, however, entails a disadvantage that such uniformity is degraded in the peripheral area of the image as compared with the central area under the influences of the COS.sup.4 law and the aberration. Since the IC sensor 4 is integrated to high density and, therefore, exhibits very weak sensitivity and very feeble output signals, it needs help of a preamplifier of high performance.
As a remedy against such a disadvantage, there has been proposed an intimate-contact reader type photo-sensor array apparatus constructed as illustrated, in fragmental section, in FIG. 2 and FIG. 3. In these figures, 5 denotes a light source made of light-emitting diodes, 6 a contact fiber opposing an original 2 for transmission and provided with a light-receiving surface on which the beams of light emitted by the light source 5 and then reflected on the original 2 impinge, 7 a sandwich fiber having embedded therein a bundle of optical fibers not shown in FIG. 3 but described in detail later, 8 a bundle of fibers embedded at prescribed positions in the contact fiber 6 and the sandwich fiber 7, 9 transparent NESA electrodes deposited on the upper surface of the sandwich fiber 7, and 10 lower electrodes made of Cr-Au alloy and deposited on the NESA electrodes 9. These lower electrodes also function as leads for wiring. By 11 is denoted a photoelectric conversion film formed across the sandwich fiber 7, the NESA electrodes 9 and the lower electrodes 10. This photoelectric conversion film 11 is formed of a Se-As-Te type amorphous thin film which is utilized as a target film in the image pickup tube called SATICON (tradename). Denoted by 12 is an upper electrode for supplying prescribed voltage to the photoelectric conversion film 11.
In the photosensor array apparatus constructed as described above, light L emitted from the light source 5 is reflected on the read surface of the original 2 for transmission to give rise to a light signal L', which is passed through a bundle 8 of optical fibers embedded in the fibers 6, 7 and led to the photo-electric conversion film 11 at which the light signal L' is converted into an electric signal. By a scanning circuits 13 such as illustrated in FIG. 4, the electric signal resulting from the conversion is sequentially subjected to switching scanning and is sequentially transmitted to an output terminal 14.
In this construction, the original 2 for transmission can be brought into nearly intimate contact with part of the image sensor which is, in this example, the bundle 8 of optical fibers.
Consequently, the lens system can be omitted, making it possible to simplify the structure and reduce the size of the device and enhance the image-resolving characteristics. Further compared with the IC sensor, this device provides a large light-receiving area per bit and permits production of a large output signal. Thus, it effectively operates with an ordinary IC without requiring any special high-performance preamplifier. Because it finds no use for the lens system, it requires no precision for the placement of the original for transmission and the sensor system. Thus, the device enjoys enhanced mass-producibility.
In order that the photosensor array apparatus of the construction described above may acquire a high image-resolving capacity, the density of the orignal-reading elements must be increased and sympathetically therewith, the number of electrodes and that of wirings for the electrodes must be increased. When an oblong sensor having a longitudinal span of about 220 mm is to be provided with read elements adapted to read the data at fixed pitches of about 1/8 mm, for example, the apparatus requires about 1700 electrodes and as many wirings. Moreover, these electrodes and wirings are required to be arranged at very small intervals of the order of about 10 microns. These requirements have been responsible for the low yield of production suffered by the device in question.
As a measure for overcoming such a disadvantage, there has been proposed a photosensor array apparatus which, as illustrated in FIG. 5, has upper electrodes 12.sub.1, 12.sub.2, . . . 12.sub.n and groups of transparent lower electrodes 10.sub.0, 10.sub.1, . . . 10.sub.9 deposited to a photo-semiconductor 15 and arranged for matrix driving. Specifically, the elongated upper electrode 12.sub.1, 12.sub.2 , . . . and 12.sub.n correspond to 1(one)-digit, 10-digit, . . . and n-digit, respectively, and a first group of lower electrodes 10.sub.0, 10.sub.1, . . . 10.sub.9, a second group of lower electrodes 10.sub.0, 10.sub.1, . . . 10.sub.9, . . . an n-th group of lower electrodes 10.sub.0, 10.sub.1, . . . and 10.sub.9 are associated with the 1(one)-digit upper electrode 12.sub.1, 10-digit upper electrode 12.sub.2, . . . and n-digit upper electrode 12.sub.n, respectively. Obviously, under the application of a suitable voltage via diodes connected as shown in FIG. 5, the upper electrodes and the lower electrodes are driven in a matrix drive fashion. For drive of 1728 bits, the FIG. 4 arrangement requires 1728+1=1729 lead wires but with the FIG. 5 arrangement, the number of lead wires can be reduced to 86 (=54+32).
In the photo-sensor array apparatus of the construction of FIG. 5, for detection of light at an overlapped portion of photo-semiconductor 15 between the upper electrodes 12 and the lower electrodes 10 as shown in FIG. 6, it is necessary to arrange the plurality of upper electrodes 12.sub.1, 12.sub.2, . . . 12.sub.n at fixed spacings of about 10 microns on the upper surface of photo-semiconductor 15. When the photo-resist method is adopted for the formation of these upper electrodes 12.sub.1, 12.sub.2, . . . 12.sub.n, the semiconductor material is degraded during the step of etching. When the stencil-mask vacuum deposition method is adopted, the deposited material seeps into the small spacings of about 10 microns separating the upper electrodes 12, posing a problem of loss of reliability of the formation of such spacings.